Vapor vent valves are used in various applications to allow vapor to vent from a container under predetermined conditions. For example, fuel vapor is vented to a carbon canister that absorbs the fuel vapor. The carbon canister is later purged of the vapor, which is then burned in the vehicle engine.
Typically, vapor vent valves are configured to block the flow of vapor from the fuel tank to the canister until a predetermined pressure of the vapor in the tank acts on the valve. The force on the vent valve due to the pressure of the vapor in the fuel tank will overcome the force of a spring biasing the vent valve to a closed position. Under those conditions, the vent valve performs an overpressure relief function. Some vapor vent valves also perform an overvacuum relief function by opening to allow vapor to flow from the vent line back into the tank when the pressure of the tank falls below a predetermined minimum pressure.